This disclosure relates to a graphene sheet and a process of preparing the same. In particular, this disclosure also relates to a process of economically manufacturing a graphene sheet having a large area and having a desired thickness.
Generally, graphite is a multi-layered stack of two-dimensional graphene sheets formed from a planar array of carbon atoms bonded into hexagonal structures. Single-layered or multi-layered graphene sheets have beneficial properties in the area of electrical conductivity.
One noticeable beneficial property is that electrons flow in an entirely unhindered fashion in a graphene sheet, which is to say that the electrons flow at the velocity of light in a vacuum. In addition, an unusual half-integer quantum Hall effect for both electrons and holes is observed in these graphene sheet.
The electron mobility in graphene sheets is about 20,000 to about 50,000 square centimeter per volt second (cm2/Vs). In addition, it is advantageous to use graphene sheets since products made from graphite are inexpensive while similar products made using carbon nanotubes are expensive due to low yields during the synthesis and the purification processes. This high cost occurs despite the fact that the carbon nanotubes themselves are inexpensive. Single wall carbon nanotubes exhibit different metallic and semiconducting properties that are dependent upon their chirality and diameter. Furthermore, single wall carbon nanotubes having similar semiconducting characteristics have different energy band gaps depending upon their chirality and diameter. Thus, in order to obtain a metallic single wall carbon nanotube composition or a semiconducting single wall carbon nanotube composition, it is desirable to separate the single wall carbon nanotubes from each other in order to obtain desired metallic or semiconducting characteristics respectively. However, separating the single wall carbon nanotubes is not a simple or inexpensive process.
On the other hand, it may be advantageous to use graphene sheets instead of carbon nanotubes since it may be possible to design a device that exhibits desired electrical characteristics by arranging the crystalline orientation in a suitable desired direction since electrical characteristics of a graphene sheet are changed according to the crystalline orientation. These characteristics of the graphene sheet may be advantageously used in carbonaceous electrical devices or carbonaceous electromagnetic devices of the future.
However, although the graphene sheet has these advantageous characteristics, a method of economically and reproducibly preparing a large-area graphene sheet has not yet been developed. Methods of preparing graphene sheets are classified into micromechanical methods and a silicon carbide (SiC) thermal decomposition method.
In the micromechanical method, a tape having a layer of adhesive on it such as, or example, a SCOTCH™ tape is applied against a graphite surface that has graphene layers preferably stacked in parallel. The graphene layers attach to the SCOTCH™ tape, which is subsequently removed from the graphite surface. The graphene layers are then removed from the SCOTCH™ tape. The graphene layers that are removed by the SCOTCH™ tape are however, not uniform in size nor do they have uniform shapes. In addition, graphene sheets having large surface areas cannot be extracted by this method. This makes their use questionable or even undesirable in certain applications.
In the SiC thermal decomposition method, a single crystal SiC is heated to remove Si by decomposing the SiC on the surface, and then residual carbon C forms on a graphene sheet. However, the single crystal SiC used in SiC thermal decomposition is very expensive, and a large-area graphene sheet cannot be easily manufactured.